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At least 19 recordsLinked to original sources
PubMed1964

STIMULANT ACTIONS OF VOLATILE ANAESTHETICS ON SMOOTH MUSCLE.

A number of volatile anaesthetics, and some compounds synthesized in the search for new anaesthetics, have been tested on guinea-pig intestinal smooth muscle in vitro. All the compounds produced a contractile response. This effect did not correlate well with convulsant activity in vivo among the compounds tested. Two kinds of stimulant effect were distinguishable: (1) Rapid, transient contractions, abolished by cocaine or lachesine; most of the anaesthetics in clinical use had this action. (2) Slow, sustained contractions, unaffected by cocaine or lachesine; this effect predominated among the fluorinated ring compounds. Hexamethonium and mepyramine did not affect the contractile response to any of the compounds. The first type of effect presumably represents excitation of postganglionic nerve cells, while the second type is a direct action on the muscle cell. The action of perfluorobenzene, which is of the latter kind, was studied further. Adrenaline and lack of calcium diminished the contraction in parallel with the contraction to histamine, which suggests that the cell membrane was the site of action; in contrast to the stimulant action of histamine or acetylcholine, the effect was highly temperature-sensitive, being almost abolished by cooling to 32 degrees C, and enhanced at 40 degrees C. The depressant action of anaesthetics on smooth muscle is affected very little by temperature changes. These findings are discussed in relation to other observations which suggest a stimulant action of volatile anaesthetics on excitable tissues. Protein denaturation is tentatively suggested as a mechanism of action.

Acetylcholine↗
PubMed1997

Divergent modes of action among cationic allosteric modulators of muscarinic M2 receptors.

We tested the hypothesis that structurally related modulators of ligand binding to muscarinic M2 receptors may not use a common recognition site. The applied test compounds are potent allosteric modulators [i.e., two bispyridinium model compounds substituted symmetrically either with phthalimidomethyl (WDuo3) or dichlorobenzyl (Duo3), a phthalimidoethyl-substituted hexamethonium compound (W84), alcuronium, and, for sake of comparison, gallamine]. As introduced by Ellis and Seidenberg as a tool to check for a common allosteric site [Mol. Pharmacol. 42:638-641 (1992)], obidoxime was used to antagonize the actions of the test compounds. The allosteric delay of the dissociation of [3H]N-methylscopolamine ([3H]NMS) from porcine heart muscarinic receptors was measured in 5 mM sodium/potassium phosphate buffer (4 mM Na2HPO4 and 1 mM KH2PO4, pH 7.4) at 23 degrees (control t1/2 = 4 min). The concentration-effect curve of obidoxime, which has a weak potency and submaximal efficacy to allosterically retard [3H]NMS dissociation, was better described with a two-site model than with a one-site model. The concentration-effect curves of the test compounds for the allosteric delay of [3H]NMS dissociation were shifted to the right in the presence of obidoxime, yet to a different extent. For WDuo3, W84, alcuronium, and gallamine, the shift induced by increasing concentrations of obidoxime was compatible with a competitive interplay. The pKb values of obidoxime against these modulators lay in a narrow range from pKb = 4.70 with gallamine to pKb = 4.16 with WDuo3. In contrast, the ability of obidoxime to shift the concentration-effect curve of Duo3 was weak (pA2 = 3.00) and not compatible with a competitive interplay. In conclusion, cationic allosteric modulators may stabilize [3H]NMS binding to M2 receptors by divergent modes of allosteric action. The findings suggest that the M2 receptor protein contains more than one allosteric recognition site on its extracellular face.

Animals↗
PubMed1977

Reexamination of carbodiimide as a possible affinity label for the acetylcholine receptor at the frog neuromuscular junction.

The effects of water-soluble carbodiimide were examined at the frog neuromuscular junction. Acetylcholine sensitivity was measured using a fluid electrode technique and intracellular recording of miniature end-plate potentials. The carbodiimide blocked synaptic sensitivity by a reversible, curare-like action. Irreversible blockade was also observed, probably due to covalent binding. The conditions of reaction and irreversibility suggest that several different residues may be attacked. The inability of cholinergic antagonists to protect the receptor from attack indicates that nonspecific sites, and not the acetylcholine binding site, are involved.

Acetylcholine↗